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SEEM3460 Tutorial

SEEM3460 Tutorial. Compiling and Debugging C programs. Compiling C programs in Unix. Compiler: cc – the native C compiler under Unix gcc – C compiler under GNU project Usage is the same, gcc is more popular To compile a C source code file, say example.c, type in: cc example.c

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SEEM3460 Tutorial

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  1. SEEM3460 Tutorial Compiling and Debugging C programs

  2. Compiling C programs in Unix • Compiler: • cc – the native C compiler under Unix • gcc – C compiler under GNU project • Usage is the same, gcc is more popular • To compile a C source code file, say example.c, type in: • cc example.c • gcc example.c • The output of both compilers (i.e. the executable) would be “a.out” by default • To override the default executable name, use “-o” flag • cc example.c –o example • gcc example.c –o example • You can name the executable as .exe or .bin file to remind yourself the nature of the file • One more tip, use “-Wall” to get some warning messages • Warning message usually indicate hidden bugs • Try to understand the error messages and warning messages. • For other flags, “man cc” or “man gcc”

  3. Compiling C programs in Unix • If there are so many compilation errors that it cannot fit into one screen. One way is to compile by the following command: • cc example.c |& more • It means that the compilation errors will be displayed screen by screen. • That is, it will display the first screen of errors and wait. • After the user examines the errors, he/she can choose to display the next screen of errors by hitting RETURN or quit by hitting Control-C. Then, the user can go back to modify the source code.

  4. Debugging C programs in Unix • Mainly 2 ways: • Add printf to trace the bug • Use debugger to find out the bug • Debugger lets you to know: • What statement or expression did the program crash on? • If an error occurs while executing a function, what line of the program contains the call to that function, and what are the parameters? • What are the values of program variables at a particular point during execution of the program? • What is the result of a particular expression in a program? • Reference: http://www.cs.princeton.edu/~benjasik/gdb/gdbtut.html

  5. Debugging C programs (2) • Debuggers available on your Unix workstations: • dbx – work for cc • gdb – work for gcc • To use debugger, add “-g” flag when compiling the program • cc –g example.c –o example • gcc –g example.c –o example • And then start the debugger by loading the executable: • dbx example (for cc) • gdb example (for gcc) • Demo on how to use a debugger (using dbx on Lab asg 1) • The demo covers only a few important commands in dbx. For detail tutorial on using dbx and gdb, google for “gdb tutorial” and “dbx tutorial” respectively.

  6. Demo commands on dbx(details see pdf tutorial notes) • help • run • rerun • trace step • trace change function`variable • trace in function • stop • step • print • whatis • whereis • quit

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